Pods on Mikunis are great, if you like tuning better than riding.
Keep the airbox and all its pieces; it's a pain to remove, but it does its job really well. (And new rubbers will make it much easier to put in and take out.)
The airbox is designed to be disposable and scheduled for replacement every 24k. You can actually pull it apart and clean the filter with foam filter cleaner; it likes that every 12k, or maybe 6k in dusty/polluted areas. You can also get replacement filter elements from third parties, but that's a waste of money IMHO 'cause the box isn't designed to last and the third party filters either don't do a very good job (K&N) or are just like the factory filter (Pipercross).
I had a bad chain when I rode from NYC to ATX; I thought it was a fueling issue (I'm on an injected bike), but it turned out my "surging" was tight and loose spots in my chain. Nice being in a dry part of the country; I'm just now replacing that replacement chain, three and a half years and 36,000 miles later.
Any of the parts fiche you might see on eBay are violations of Triumph's copyright, and talking about that's a no-no in this forum. (We use copyrighted Triumph logos with permission and generally have a close relationship with Triumph, and would not want to jeopardize that. Bike Bandit has online fiche you can use, but they have BB part numbers instead of Triumph. Ling's in the UK, AKA World of Triumph, show you the Triumph part number in the shopping cart.
Springs work the same upside down as they do right side up.
Like Flattrack Loon says, get the Haynes manual. $35 well spent, and you can find it on eBay if Amazon's out of stock. "Triumph Triples and Fours" is the title.
Speaking of... Have you got a triple or a four?